Regulation T

What Is Regulation T?

Regulation T, often called Reg T, is the Federal Reserve rule governing credit that brokers and dealers extend to customers for securities transactions. It is best known for initial margin requirements in margin accounts.

When an investor buys securities on margin, the broker lends part of the purchase price and the investor supplies the rest. Regulation T sets the federal framework for how that initial credit can be extended, when payment is due, and how certain broker-dealer credit accounts operate.

How Reg T Margin Works

In a margin account, the investor uses some personal equity and some borrowed money to purchase securities. Regulation T establishes the federal initial margin framework for the transaction. The commonly cited initial margin level for many margin stock purchases is 50%, meaning the investor must provide at least half of the purchase price, though specific treatment depends on the security and account context.

Initial margin is not the same as maintenance margin. Initial margin applies when the position is established. Maintenance margin governs how much equity must remain in the account after prices move. Maintenance requirements often come from self-regulatory organization rules and brokerage house requirements, and firms may demand more than the regulatory minimum.

What Investors See in Practice

Regulation T shows up when a brokerage account allows margin borrowing, when a trade must be paid for by a deadline, when a security is not marginable, or when a broker restricts how much a customer can borrow against a position. It also matters when an investor uses margin to buy stocks, ETFs, options strategies, or other securities with special margin treatment.

Margin can make a portfolio look more flexible because cash is not required for the entire purchase price. The cost is leverage. If the investment falls, losses are magnified and the broker can issue a margin call, sell securities, or change house requirements.

Regulation T Versus Regulation U

Regulation T applies to brokers and dealers. Regulation U applies to banks and certain other lenders when loans secured by margin stock are used to buy or carry margin stock. The distinction helps determine which rule applies to a brokerage margin account versus a bank loan secured by a securities portfolio.

For an investor, the practical result is that borrowing against securities can be governed by different rules depending on who lends the money, what collateral is pledged, and how the proceeds are used.

Margin Risk in a Falling Market

Regulation T can make the initial trade possible, but it does not protect the investor from later price moves. If the securities fall, the investor's equity declines faster than it would in an unleveraged account. The broker may require more cash or securities, restrict trading, or sell positions without waiting for the investor's preferred timing.

Interest cost also changes the return hurdle. A margined position needs to earn enough to cover borrowing costs and still compensate for the added risk. That is why margin is usually a risk-management decision, not merely a way to increase buying power.

The Bottom Line

Regulation T is the core federal margin rule for broker-dealer credit. It helps set the borrowing framework for margin accounts, but investors still need to account for maintenance rules, broker house requirements, interest costs, and forced-sale risk. The rule defines the starting gate for leverage, not the full risk of carrying it.